Train in ballroom dancing by taking private lessons or group classes. Research local dance studios in your area that offer ballroom dancing lessons and enquire about classes that suit your level of expertise. Tell your dance teacher you wish to eventually compete in ballroom dancing competitions so she knows how exactly to train you.
Find a dancing partner who dances at your same level. Your partner should be someone who you are compatible with, as you will spend a lot of time together practicing. Also, competition judges often look for chemistry between partners during a dance, so make sure it's someone you're comfortable with.
Sign up to take part in a ballroom dancing competition once you and your dance trainer feel you're ready. Choose a competition for beginners first, then choose more advanced competitions once you feel you're ready. Research ballroom dancing competitions, also referred to as Dance Sport competitions, in your area by asking staff at your local dance studio or by using an online search engine. The website AccessDance.com provides a search tool where you can search for dance competitions in your sate (see Resources). The website USADance.com also provides resources on competitive ballroom dancing in their "forms and resources" section (see Resources).